Continuous sitting at the workplace increases the risk health problems including cardio-metabolic diseases and mortality. A novel way to reduce workplace sedentary behavior is to modify the workspace using treadmill and sit-to-stand workstations. These workstations allow sedentary office workers to replace sitting time with slow walking and/or standing while simultaneously performing work. However, there is limited empirical evidence on the health benefits of using treadmill and sit-to-stand workstations at the workplace. The long-term goal is to decrease sedentary behavior in office workers and improve overall health. The objective of this application is to determine the effects of decreasing workplace sedentary behavior using treadmill and sit-to-stand workstations on the health of overweight office workers, who are at high risk for chronic cardiovascular and metabolic diseases. The central hypothesis is that decreasing workplace sedentary behavior using these workstations will improve overall health in study participants. This hypothesis is based on preliminary findings from the applicants' where sedentary overweight office workers using treadmill workstations for 9-months improved cardiovascular and metabolic health. The central hypothesis will be tested through two specific aims: (1) To conduct a 12-month, cluster-randomized trial with an intent-to-treat design to determine the effects of using treadmill and sit to-stand workstations at the workplace on health variables in overweight office workers (N=66) with seated desk jobs and (2) to compare the efficacies of treadmill and sit-to-stand workstations in decreasing workplace sedentary behavior. For aim 1, the effects of using these workstations will be examined by measuring changes in weight, cardiovascular and metabolic health variables (blood flow hemodynamics, blood biomarkers, and body composition), musculoskeletal discomfort, psychological affect and job stress. For aim 2, change in time spent sitting, standing and walking will be measured using wearable non-invasive acceleration sensors. The approach is innovative because the study aims to maximize the gains from the interventions through employer support, measurement of health variables sensitive to change in sedentary behavior and the use of advanced sensors, which accurately measures sedentary behavior and also provides real-time feedback to break prolonged sitting. A significant output of this project may be the development of evidence-based strategies and recommendations that modify the office environment to decrease workplace sedentary behavior. A significant outcome of decreasing workplace sedentary behavior may be a decrease in chronic illness in office workers. These potential outputs and outcomes are in line with NIOSH's r2p: Research to Practice' initiative, which aims to translate NIOSH-generated knowledge and interventions to prevent and eliminate occupational illness. This project will address the NORA's Total Worker Health Initiative by integrating the work environment, employer and employee to promote overall worker health. This application is also pertinent to NIOSH's Prevention through Design program portfolio aiming to retrofit work environments with equipment that can prevent illness.